Prostate and lung cancers are the most frequently occurring cancers in U.S. men. Lung cancer recently replaced breast cancer as most common cause of cancer death among American women. Despite its prevalence, prostate cancer has not been extensively studied; its etiology remains relatively obscure. Hypotheses for the causes of prostate cancer include the effect of androgenic hormones, diet and nutrition, sexual activity, infectious agents, history of benign prostate disease and vasectomy, occupational exposures, and family history. Tobacco smoking has been established as the major environmental risk factor for lung cancer. Other factors that may act independently or in combination with tobacco use include diet and nutrition, family history, and genetic factors including oncogene, suppressor gene, and metabolic gene polymorphisms. We propose nested case-control studies of the etiology of these tumors in prostate and lung cancer cases and suitable controls selected from a population enrolled in an experimental program of screening for these and other cancers. The proposed project will provide support for the conduct of case-control studies of prostate and lung cancer to be conducted by the National Cancer Institute. The subjects for this study will be selected from a population enrolled in an experimental program of screening for these and other cancers. The screening program will be carried out by the NCI at several Screening Centers (SCs) and will be coordinated by a Study Coordinating and Data Management Center (CC). The epidemiologic study of risk factors for prostate and lung cancer will be carried out in coordination with the Scs and CC. The major objectives are: (10 to develop data collection instruments for all study subjects at baseline and for selected subjects included in the nested case-control studies of cancer; (2) to develop management systems for the efficient and timely transfer of information from the Scs and the CC to the epidemiologic study contractor; and (30 to investigate biologic and environmental risk factors for prostate and lung cancer in nested case- control studies in a population being screened for these diseases.